The steam generators of pressurized water nuclear reactors contain a tube bundle, the ends of the tubes passing through a tube plate and opening into a water box of hemispherical shape which provides for the distribution in the tubes of pressurized water coming from the reactor vessel, and the recovery of the pressurized water which has circulated through the tubes of the bundle.
During the operation of the steam generator, some of the tubes of the bundle can be caused to crack, through the effect of mechanical or thermal stresses or through the effect of corrosion. To remedy this deterioration of the tubes, processes and devices have been proposed, whereby the tubes may be lined with a sleeve introduced into the tube in the cracked region, and fixed to the inner wall of the tube in a resistant and leakproof manner.
It may be necessary to complete the lining by welding one of the ends of the sleeve to the tube. This welding operation is carried out with an orbital type inert-gas arc welding machine containing a tungsten electrode attached to a tubular support which is introduced into the tube and the sleeve so as to present the electrode in the desired region, the electrode being rotated about an axis coincident with the axis of the tube.
Such a welding machine, which is operated from the water box of the steam generator, contains a welding sheath through which the tubular support for the electrode passes, and which can be introduced into the tube to perform the welding of the sleeve. The welding machine also contains a motorization and fluid distribution assembly, for roating the tubular support for the electrode and for supplying it with cooling water, as well as for supplying the welding region with inert gas.
Between the welding sheath and the motorization and distribution assembly, there is interposed a linking housing through which passes a transmission shaft connected to the motorization device, enabling the electrode support to be driven in rotation, and through which pass various channels for the circulation of fluids. The linking housing also enables a conductor to be passed through, for supplying the electrode with electric current.
The welding machine assembly, comprising the sheath, the linking housing and the means of motorization and distribution, is of considerable length, so that sufficient clearance must be provided inside the water box.
For the tubes of the steam generator situated in the central portion of the bundle, the height of the water box is amply sufficient to permit the welding machine to be moved in a direction perpendicular to the tubes. In contrast, as regards the peripheral tubes, the free height perpendicular to these tubes, up to the hemispherical wall of the water box, can be altogether insufficient to permit the insertion of the electrode support and the sheath into the tube and for carrying out the orbital welding of the end of a corresponding repair sleeve.
A machine or equipment which made it possible to weld the end of a sleeve in a peripheral tube of the steam generator was not known to date.